1. Field of the Invention
This invention relates to fluid-handling apparatus, in particular for filling a carton.
2. Description of the Prior Art
European Patent Publication No. 0013132 discloses an aseptic packaging machine which includes a chain conveyor conveying cartons along a path in an aseptic chamber including an advance leg and a return leg each extending along the machine. Ultra-violet germicidal lamps extend over at least a major portion of the advance leg. Aseptic liquid is fed into the cartons by a filling device. After filling, the cartons are top-heated and sealed by a top-heating device and a top-sealing device. The only non-aseptic matter deliberately introduced into the chamber is the cartons. The chamber is cleaned internally by cleaning fluid from spray nozzles. The carton entry to and exit from the chamber have aseptic air curtains.
The filling device is particularly designed to prevent microbes obtaining access to the aseptic liquid product being supplied to the aseptic chamber. The filling device includes a mounting frame which mounts four stainless steel reciprocatory bellows having bottom walls which are reciprocatorally driven by respective reciprocatory plungers and having top flanges fixed to respective lower limbs of fixed T-unions. Respective upper limbs of the unions contain respective spring-loaded, non-return, inlet valves which open to allow downward flow through the limbs. Intermediate limbs of the respective unions are connected to respective arcuate pipes which curve downwardly towards the path of the cartons and which at their lower ends are connected to respective outlet nozzles which contain respective spring-loaded, non-return, outlet valves. The chains advance the cartons stepwise directly below the line of nozzles and a selected number of the bellows are operated each to deliver a predetermined dosage of long-life milk to the vertically upright cartons, the number of bellows operated being dependent upon the nominal capacity of the cartons. Thus, with each bellows being pre-set to deliver a half pint at each reciprocation, all four bellows are operated for cartons which can each hold one quart. On each bellows performing a pressure stroke, because the inlet valve in its union is held closed by its spring and by the milk pressure, the inlet valve is automatically opened against the action of its spring so that the bellows can draw in milk from an expansion chamber.
In a widely used design applicable to that machine, the nozzle would comprise a tubular housing and a valve member in the housing. The tubular housing is formed internally, at a location spaced an appreciable distance above its lower extremity, with a valve seat in the form of a downwardly-facing, frusto-conical surface. Immediately beyond this surface, the housing widens to form an expansion space and then narrows again to continue downwards as a cylindrical bore. The valve member comprises a disc-form driving part, a stem extending downwards from the driving part, and a closure part fixed to the lower end of the stem and having a frusto-conical surface co-axial with the housing and arranged to come face-to-face with the valve seat. This latter surface is formed with a co-axial annular groove containing an elastomeric O-ring for sealing against the valve seat. The valve member is movable axially between a closed condition in which the closure part is within the tubular housing and acts sealingly on the valve seat by way of the O-ring and an open condition in which the closure part is still within the housing but spaced downwards from the valve seat. The valve member is encircled by a closing spring urging the closure part into its closed position. The valve member is opened by the pressure differential between the pressure of the liquid upstream of the driving part and the pressure downstream of the driving part. When this pressure differential is sufficiently high to overcome the pressure of the spring, the valve member opens. The driving part is considerably smaller in diameter than is the O-ring. The extent of compression of the spring determines the extent of opening of the valve member. The valve member includes a second stem extending downwardly from the closure part and widening at its lower end region to obturate the cylindrical bore in the closed condition of the valve member. In the open condition, the lower extremity of this stem is spaced downwards from the housing and the liquid can flow down therebetween. The valve member also includes two or more fins which extend upwardly from the lower end of the second stem and slide on the surface of the cylindrical bore. Were it not for the fins, in the open condition of the valve member, the liquid would flow from the valve member as a substantially unbroken tube of liquid. This would mean that air trapped within the tube of liquid and increasingly under pressure as the liquid level in the carton climbs would be forced to break through the tube of liquid to escape and in so doing would disturb the smooth flow of the liquid into the carton and cause splashing of liquid beyond the carton. The presence of the fins ensures that corresponding vents are formed along the tube of liquid through which vents air can flow without disturbing the flow of the liquid.
The machine described above has a number of disadvantages in connection with its filling device.
There is an optimum range of rate of flow of liquid into the carton, but the flow rate is dependent upon the pressure under which the liquid is being urged past the closure part, which is approximately the same as the opening pressure of the valve member. However, the opening pressure is dependent upon the effective area of the valve member acted upon by the liquid pressure. Therefore a relatively small effective area requires a relatively high opening pressure which involves an undesirably high rate of flow of liquid into the carton and in practice a high degree of turbulence. A further disadvantage is that the small effective area over which the liquid pressure acts to open the valve member may produce an opening force which is insufficient to prevent hunting of the valve member, which results in an unsteady flow of liquid into the carton, but a steady, smooth flow is desirable. The use of an O-ring mounted in a groove provides, between the ring and the wall of the groove, very narrow crevices in which foreign matter, including microbes, can gather, but which are almost inaccessible to cleaning fluid. In addition, the housing has an appreciable area of its internal surface below the annulus of sealing between the valve seat and the O-ring, and this area is normally wetted by contact with the liquid from the open outlet valve, so that there is a risk that liquid will drip from the nozzle even when the outlet valve has been fully closed and thus drip onto the exteriors of cartons or onto the conveyor forwarding the cartons. Such dripping is obviously undesirable. Furthermore, unsteadiness of flow can also occur because the maximum extent of opening of the closure part is variable. Stainless steel has a limited fatigue life on being flexed and is therefore liable to fracture. Fracturing of the bellows allows penetration of bacteria and/or leakage of liquid. Moreover, stainless steel is a relatively expensive material and is relatively expensive to fabricate into a bellows. Finally, the arrangement whereby the liquid passes via a union into a pumping bellows and then partly back through the union towards a nozzle is difficult to clean and to purge of cleaning fluid.
A variable area valve disclosed in U.S. Pat. No. 3,022,954 includes a valve stem formed with flutes which are either arranged in axial planes or arranged helically around the stem. In both cases, they terminate at such a distance upstream of the annulus of sealing between the valve closure member and the valve seat that the streams of liquid among the flutes reunite upstream of the downstream extremity of the valve closure member, so that the liquid flows from the valve member as a substantially unbroken tube of liquid.
British Pat. No. 1335007 discloses a metering device for liquids and pastes, comprising at least one unit having an inlet valve and an outlet valve which is connected by a bellows of polytetrafluoroethylene, for example, to the inlet valve and which has a valve body in the form of a diaphragm carrying an outlet nozzle, the two ends of the bellows of each such unit being clamped to two spaced horizontal plates which are relatively movable through an adjustable distance, there being some means to open the inlet valve when the plates are moving apart and to close the inlet valve when the plates are moving together, the outlet valve being arranged to open when the plates are moving together and to close when the plates are moving apart. The inlet valve can consist of a stem extending through the wall of ducting leading to the bellows and provided at its end within the ducting with a frusto-conical valve plate which cooperates with a similarly shaped valve seat formed by an internal shoulder of the ducting. The diaphragm of the outlet valve can be arranged to be held in a closed position by compressed air introduced around the nozzle and beneath the diaphragm. However, the diaphragm of the outlet valve may instead be prestressed so that it is bent upwardly and not downwardly when it is relaxed. In this instance, it is possible to dispense with the compressed air control, since the outlet valve is always in the closed position except when the lower plate is being moved upwardly. However, in the latter circumstance, i.e. when the bellows is being compressed, the pressure of the liquid in the bellows overcomes the prestress of the diaphragm, so that the outlet valve opens and allows the liquid to escape. However, such an arrangement has the disadvantage of lesser operational reliabiity than that utilizing compressed air control. The inlet valve, which is angled, may be replaced by a vertical-axis valve which, if required, may also be provided with a pneumatic control arrangement.
The metering device just described has the disadvantage that polytetrafluoroethylene is a relatively expensive material and very expensive to fabricate into a bellows shape. The device also has the disadvantage that either the nozzle and its supporting plate have to be reciprocated vertically with the nozzle being moved in and out of the carton, which involves a relatively slow cycle of lowering and lifting, or the upper plate, with at least a significant section of the ducting, has to be lifted and lowered, which again involves not only a relatively slow cycle of movement, but also a relatively complicated mounting arrangement.
U.S. Pat. No. 2,962,227 discloses a fuel injection nozzle comprising a tubular body internally screwthreaded to receive a connector nipple having an internal bore terminating at its lower end in a cylindrical chamber. Located in the chamber is a detachable tubular valve housing through which extends a stem carrying at its lower end a valve closure member of apparently frustoconical form cooperating with an apparently frustoconical valve seat within the outlet of the housing. The upper end of the stem is externally screwthreaded to receive an internally screwthreaded metal disc formed with angularly drilled apertures each inclined inwardly and downwardly and having its lower end spaced from the stem. These apertures permit fuel to pass to beneath the disc. The valve stem is maintained in position on the disc by a lock nut. The central bore of the valve housing is counterbored to receive a distance piece and a helical spring bearing at its lower end on the distance piece and at its upper end against the underside of the disc. In the bottom of the chamber and underneath the disc is a ring of elastomeric material which is normally separated from the underside of the disc by a small free space. When the nozzle is operated at low delivery rates, fuel enters the chamber and passes through the apertures in the disc and down to the valve seat. The fuel pressure thereby built up downstream of the disc ultimately forces the valve closure member to open against the force of the spring, so that the fuel is injected, but a small free space still remains between the elastomeric ring and the disc. However, at high delivery rates, the valve opens more, thus pressing the disc against the ring and thereby closing the free space. Thereupon, less of the underside of the disc is exposed to the fuel pressure, so that the valve is maintained more reliably in that position.
With the fuel injection nozzle just described, dirt and bacteria can accumulate in places where cleaning fluid passed through the nozzle would not wash them away, for example, in the screwthreading between the disc and the stem.